Commercially available combustion meters generally employ a temperature sensor that monitors the heat effect from the catalytic-heterogeneous combustion of fuels with excess oxygen. Most commonly used is the hot wire technique, which employes a resistance heated noble metal filament commonly made of platinum. If the filament is heated in an atmosphere containing fuels and sufficient oxygen for combustion is present, the oxidation of the fuels is catalyzed at the metal-gas interface. The heat released by the combustion raises the temperature of the wire and thereby also increases the resistance. Typically the wire forms one leg of an electrical bridge configuration with an identical reference wire located in a fuel free atmosphere. The imbalance of the bridge circuit resulting from heating of the filament produces a measurement of the fuel concentration.
The disadvantage of hot wire detector is its relatively low sensitivity which limits the usefulness for monitoring low fuel concentrations, i.e., less than one percent.